1. Field of the Invention
The invention relates to a method of bonding a porous fibrous web to a substrate and articles made thereby, and more particularly to a process whereby and products wherein a porous web is affixed to a substrate with excellent bond strength utilizing a very low level of hot-melt adhesive, the bond being essentially invisible and the porous web maintaining its flexibility and fluid transparency.
2. Description of the Prior Art
The process of the present invention may be applied in any instance where it is desired to provide a laminated product, at least one lamination of which comprises a fluid-porous, fibrous sheet. An excellent example of such a product is an integral disposable diaper. While not intended to be so limited, for purposes of exemplary showing the present invention will be described in its application to the manufacture of integral disposable diapers.
Prior art workers have devised a number of different types of integral disposable diapers. Generally, however, such diapers comprise three basic parts: a moisture pervious topsheet intended to lie adjacent the body of the wearer, a moisture proof backsheet and an absorbent core therebetween. Examples of such disposable diapers are taught in U.S. Pat. Nos. Re. 26,151 and 3,860,003. The absorbent core may or may not be provided with a layer of high wet strength tissue on one or both of its faces.
In a typical practice, a topsheet may be provide with an extruded bead or stripe of hot-melt adhesive along each of its edges. These edges are folded about the edges of the absorbent core and are adhered to the underside of the absorbent core. In somewhat similar fashion, extruded hot-melt adhesive stripes or beads are located on the backsheet inset from and parallel to its longitudinal edges. The folded edges of the topsheet are adhered to the backsheet by means of these last mentioned adhesive stripes. Additional adhesive stripes or beads may be provided on the topsheet to join it to the backsheet at the waste band areas of the diaper.
In another approach, the backsheet is provided with a plurality of longitudinally extending hot-melt adhesive stripes or beads in parallel spaced relationship. The absorbent core is applied to the backsheet and adhered thereto by the adhesive stripes. The topsheet is next applied, being adhered to those edge portions of the backsheet which extend beyond the core.
The above approaches utilizing hot-melt adhesive stripes or beads result in certain deficiencies. First of all, the adhesive usage is relatively high with respect to the area actually bonded and the adhesive stripes or beads are apparent and unsightly. At the positions of the adhesive stripes or beads, the softness of the product is reduced. As a result, much work has been directed to making the stripes or beads of hot-melt adhesive as thin as possible so as to be as flexible as possible. Wherever the adhesive stripes or beads are applied to, or are in contact with, the porous, fibrous topsheet, the porosity of the topsheet is lost or seriously effected. Furthermore, in products requiring large areas of bonding a multiplicity of adhesive stripes are required in close proximity thereby greatly exaggerating the above enumerated deficiencies. Finally, in those prior art approaches wherein only peripheral gluing of the diaper components is practiced, the absorbent core may shift or bunch due to movement of the wearer.
The present invention provides a process whereby and a product wherein a hot-melt adhesive may be applied to even large areas of the porous, fibrous topsheet and the topsheet adhered to the substrate (the backsheet and/or the absorbent core). Hot-melt adhesive applied to the porous, fibrous topsheet in the manner taught herein provides an excellent fiber-to-adhesive bond with very good peel and creep bond characteristics to substrates. Nevertheless, the adhesive is substantially invisible; the softness of the product is retained and the moisture transparency-permeability of the topsheet is reduced only by 5% or less. Where the disposable diaper has cut longitudinal edges (as in diapers of the type taught in the above mentioned U.S. Pat. No. 3,860,003) the entire edge portions of the diaper can be laminated producing neater and more easily cut edges.